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Hybrid Zones

Hybrid Zones

Hybrid zones are narrow regions where two closely related species interact, mate, and produce hybrids. Relative to either parent species, hybrids may possess distinct phenotypic or genetic differences that impact their survival and reproductive success. The genetic variances introduced by hybridization influence species diversity and speciation processes within the hybrid zone.

Genetics of Speciation

Genetics of Speciation

Speciation is the evolutionary process resulting in the formation of new, distinct species—groups of reproductively isolated populations.

Background and Environment Affect Phenotype

Background and Environment Affect Phenotype

Although the genetic makeup of an organism plays a major role in determining the phenotype, there are also several environmental factors, such as temperature, oxygen availability, presence of mutagens, that can alter an organism’s phenotype.
An example of how genetic background affects phenotype can be seen in horses. The Extension gene in horses is responsible for their coat color. A wild-type gene (EE) produces black pigment in the coat, while a mutant gene (ee) produces red pigment. A...

Exon Recombination

Exon Recombination

The evolution of new genes is critical for speciation. Exon recombination, also known as exon shuffling or domain shuffling, is an important means of new gene formation. It is observed across vertebrates, invertebrates, and in some plants such as potatoes and sunflowers. During exon recombination, exons from the same or different genes recombine and produce new exon-intron combinations, which might evolve into new genes.
Exon shuffling follows “splice frame rules.” Each exon...

Incomplete Dominance

Incomplete Dominance

Gregor Mendel's work (1822 - 1884) was primarily focused on pea plants. Through his initial experiments, he determined that every gene in a diploid cell has two variants called alleles inherited from each parent. He suggested that amongst these two alleles, one allele is dominant in character and the other recessive. The combination of alleles determines the phenotype of a gene in an organism.

Gene Flow

Gene Flow

Gene flow is the transfer of genes among populations, resulting from either the dispersal of gametes or from the migration of individuals.

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Dissection and Flat-mounting of the Threespine Stickleback Branchial Skeleton

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Riverscape genetics of the orangethroat darter complex.

John T Belcik^1,2, Mary V Ashley¹

¹Department of Biological Sciences, University of Illinois at Chicago, Chicago, Illinois, USA.

Journal of Fish Biology

|November 16, 2023

Summary

Orangethroat darters (Ceasia) in the US show surprising genetic structure in glaciated areas, with two distinct clusters in Etheostoma spectabile. Unglaciated regions exhibited less genetic differentiation, suggesting complex post-glacial gene flow.

Keywords:

AIC Ceasia DNA microsatellites biogeography cluster analysis glacial refugia

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Area of Science:

Ichthyology
Evolutionary Biology
Conservation Genetics

Background:

The orangethroat darter species complex (Ceasia) is widespread across the Central and Southern United States.
This complex includes up to 15 species, with varying distributions in glaciated and unglaciated regions.
Species diversity and endemism are notably higher in the unglaciated Central Highlands.

Purpose of the Study:

To evaluate genetic diversity and structure within the Ceasia complex.
To investigate pre- and post-glacial range dynamics.
To test the hypothesis of stronger genetic differentiation in unglaciated areas.

Main Methods:

Microsatellite genotyping of 384 darters from 52 sites.
Analysis of genetic diversity and population structure.
Comparison of genetic data with geographical distribution and species identification.

Main Results:

Two distinct genetic clusters of Etheostoma spectabile were identified in glaciated regions (Illinois River basin and Wabash/Great Lakes tributaries).
These clusters suggest expansion from two isolated glacial refugia with limited post-glacial gene flow.
Fish from unglaciated regions showed less genetic differentiation, with some species (E. burri, E. uniporum) not genetically distinct from E. spectabile.

Conclusions:

Glaciated regions exhibit stronger genetic differentiation than anticipated, indicating isolation from distinct glacial refugia.
Hybridization and introgression in the Central Highlands may complicate species delineation in this high-diversity area.
Further research is needed to clarify species boundaries and evolutionary history within the Ceasia complex.